The invention relates to heat exchangers and to the manufacturing processes that are dedicated thereto.
The invention relates more particularly to a process for manufacturing a heat exchanger of the brazed type, in which a surface treatment is carried out.
Such a process is used for example for manufacturing evaporators used in motor vehicle air-conditioning circuits.
The invention also relates to a heat exchanger manufactured according to this manufacturing process, in particular an evaporator for a motor vehicle air-conditioning circuit.
Surface treatments designed to give the surface of a heat exchanger specific properties are known. For example, the surface in contact with the ambient air is treated so as to prevent or suppress the growth of microorganisms on this surface, these microorganisms themselves being a source of or environment conducive to perceptible smells during operation of this exchanger.
The surface treatment is generally carried out by immersing the heat exchanger in a series of baths alternately containing active agents, intended to give the surface the desired properties, and rinsing liquids, intended to prepare the heat exchanger for the next bath. It is also known practice to apply a coating by spraying.
Thus, document U.S. Pat. No. 5,376,411 suggests applying a coating to a heat exchanger by immersing it in a bath for producing a hydrophilic film and then applying an antimicrobial agent to this coating before the latter has completely dried.
Moreover, document EP 1 201 788 discloses the application of two films having anticorrosive and hydrophilic properties to the surface of an aluminum heat exchanger.
It should be noted that in both these documents the application of a coating is performed only once the heat exchanger has been assembled and brazed. This is because the coatings described are not capable of withstanding high temperatures, such as those encountered during the hard brazing process. Hard brazing is brazing carried out at temperatures above 400° C. and possibly up to 630° C.
These manufacturing processes and the heat exchangers that result therefrom have many drawbacks. In the first place, since the surface treatment is carried out after the brazing, it is necessary to treat the heat exchanger as a single part. This involves the treatment of surfaces that would not necessarily require it, and therefore a loss of productivity.
Secondly, the requirement of treating the entire heat exchanger means that there is no control of the amount of coating applied to each component of the heat exchanger.
Finally, the need to prepare the heat exchanger and to remove the brazing residues before the baths or the spraying tends to reduce the productivity of the production line.